The present invention relates generally to the gasification of carbonaceous materials by pyrolysis for the production of hydrocarbon liquids and combustible gases, and more particularly to the preparation of high quality liquid hydrocarbon and combustible gas products by the pyrolysis of coal or oil shale at relatively low temperatures in the presence of calcium compounds.
Coal and oil shale have been subjected to various thermal decomposition procedures for providing combustible product gases and hydrocarbon liquids which can be used as fuels or as fuel precursors. For example, coal has been gasified and liquified by externally applied heat or pyrolysis of coal constituents.
Of the several techniques utilized to produce liquids from coal some of the better known include such processes as the direct liquefaction by hydrogenation, indirect liquefaction by Fischer-Tropsch processes, and pyrolysis by employing high heating rates such as hydropyrolysis. These processes are relatively complex and expensive to operate so as to provide a relatively high-cost product as compared to other sources of hydrocarbon liquids derived from petroleum. Thus, the direct and indirect coal liquefaction procedures that provide acceptable liquid hydrocarbon products which can be used directly as fuels or which can be further refined to provide more acceptable fuel products are presently considered to be excessively costly procedures so as to detract from their utilization at the present time. Pyrolysis processes using rapid heating techniques have been found to increase the yield of product liquids but the resulting liquids are of relatively poor quality due to the low hydrogen to carbon ratios (H/C) and high sulfur content which necessitates costly upgrading.